<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        span {
            background: lightblue;
        }

        div span {
            background: lawngreen;
        }
    </style>

</head>
<body>

<div>
    <span class="span1">span1
        <span class="span2">span2</span>
    </span>
</div>
<span class="span3">span3</span>

<img src="./img/04.png" alt="Test"><!--这里存放的是课堂图片-->
</body>
</html>